maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/visitor/PathRecordingDependencyVisitor.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.eclipse.aether.util.graph.visitor;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import org.eclipse.aether.graph.DependencyFilter;
import org.eclipse.aether.graph.DependencyNode;
import org.eclipse.aether.graph.DependencyVisitor;

/**
 * A dependency visitor that records all paths leading to nodes matching a certain filter criteria.
 */
public final class PathRecordingDependencyVisitor implements DependencyVisitor {

    private final DependencyFilter filter;

    private final List<List<DependencyNode>> paths;

    private final Stack<DependencyNode> parents;

    private final boolean excludeChildrenOfMatches;

    /**
     * Creates a new visitor that uses the specified filter to identify terminal nodes of interesting paths. The visitor
     * will not search for paths going beyond an already matched node.
     *
     * @param filter The filter used to select terminal nodes of paths to record, may be {@code null} to match any node.
     */
    public PathRecordingDependencyVisitor(DependencyFilter filter) {
        this(filter, true);
    }

    /**
     * Creates a new visitor that uses the specified filter to identify terminal nodes of interesting paths.
     *
     * @param filter The filter used to select terminal nodes of paths to record, may be {@code null} to match any node.
     * @param excludeChildrenOfMatches Flag controlling whether children of matched nodes should be excluded from the
     *            traversal, thereby ignoring any potential paths to other matching nodes beneath a matching ancestor
     *            node. If {@code true}, all recorded paths will have only one matching node (namely the terminal node),
     *            if {@code false} a recorded path can consist of multiple matching nodes.
     */
    public PathRecordingDependencyVisitor(DependencyFilter filter, boolean excludeChildrenOfMatches) {
        this.filter = filter;
        this.excludeChildrenOfMatches = excludeChildrenOfMatches;
        paths = new ArrayList<>();
        parents = new Stack<>();
    }

    /**
     * Gets the filter being used to select terminal nodes.
     *
     * @return The filter being used or {@code null} if none.
     */
    public DependencyFilter getFilter() {
        return filter;
    }

    /**
     * Gets the paths leading to nodes matching the filter that have been recorded during the graph visit. A path is
     * given as a sequence of nodes, starting with the root node of the graph and ending with a node that matched the
     * filter.
     *
     * @return The recorded paths, never {@code null}.
     */
    public List<List<DependencyNode>> getPaths() {
        return paths;
    }

    @Override
    public boolean visitEnter(DependencyNode node) {
        boolean accept = filter == null || filter.accept(node, parents);

        boolean hasDuplicateNodeInParent = parents.contains(node);
        parents.push(node);

        if (accept) {
            DependencyNode[] path = new DependencyNode[parents.size()];
            for (int i = 0, n = parents.size(); i < n; i++) {
                path[n - i - 1] = parents.get(i);
            }
            paths.add(Arrays.asList(path));

            if (excludeChildrenOfMatches) {
                return false;
            }
        }

        return !hasDuplicateNodeInParent;
    }

    @Override
    public boolean visitLeave(DependencyNode node) {
        parents.pop();

        return true;
    }
}